1. Field of the Invention
The present invention relates to a bandwidth management apparatus for allocating bandwidths to links to be used for transmission of communication information according to a call setup procedure and an address resolution assistance apparatus for performing mutual conversion between the telephone number and the address of the originating party of a call in a packet-switched network where communication information is transmitted as a sequence of datagrams. The invention also relates to a bandwidth managing method and an address resolution assisting method for realizing the above bandwidth management apparatus and the address resolution assisting apparatus, respectively.
2. Description of the Related Art
The Internet, which has advanced rapidly in recent years, is becoming a base of the management strategy of each of a number of companies as the cost of transmission of multimedia including images, speech, and video decreases and its speed increases. The information processing technology and the communication technology that implement the Internet are being studied and developed enthusiastically and becoming a base that is indispensable for the advancement of the network computing era.
In many corporate networks (including intranets and extranets) using the above technologies, a speech signal of a telephony call is transmitted as a sequence of datagrams such as IP packets under application of the VolP.
FIG. 14 shows the configuration of an exemplary network to which the VolP is applied.
In FIG. 14, LANs 61-11 and 61-12 (not shown for simplicity) are provided in respective bases 60-11 and 60-12 (bases here include sites) and respectively connected to first and second ports of a router 62-1. A third port of the router 62-1 is connected to a first port of a router 62-2 via an internode link 63-12 that is a link. LANs (will be denoted below by symbols “61-21” and “61-22” but are not shown in FIG. 14 for simplicity) that are provided in respective bases 60-21 and 60-22 are connected to second and third ports of the router 62-2. A fourth port of the router 62-2 is connected to a first port of a router 62-3 via an internode link 63-23. LANs (will be denoted below by symbols “61-31” and “61-32” but are not shown in FIG. 14 for simplicity) that are provided in respective bases 60-31 and 60-32 are connected to second and third ports of the router 62-3.
In the base 60-11, an endpoint 70-11 and a gatekeeper 80-11 are connected to the LAN 61-11.
The endpoint 70-11 is composed of the following components:                A terminal processing part 71-11 that is connected to the LAN 61-11.        A protocol converting part 72-11 that is connected in cascade to the terminal processing part 71-11.        An interfacing part 73-11 that is connected in cascade to the protocol converting part 72-11 and connected to a telephone network (not shown; may be an ISDN or a PBX) or a telephone set (not shown).        
In the following description, the set of the terminal processing part 71-11, the protocol converting part 72-11, and the interfacing part 73-11 will be called “gateway” and will be given a symbol “70GW-11.”
The gatekeeper 80-11 is composed of the following components:                An interfacing part 81-11 that is connected to the LAN 61-11.        A processor 82-11 having a bus or port that is connected to the interfacing part 81-11.        A database 83-11 that is accessed by the processor 82-11 when necessary.        
The database 83-11 is composed of an address table 84-11 and a state management table 85-11 that will be described below.
As shown in FIG. 15, pairs of a telephone number (includes a unique office code that is given to a gateway that accommodates an accommodated terminal; or may be formed by only the office code) and an IP address that are given to each of the telephone sets that are connected to the interfacing part 73-11 or the telephone sets accommodated by a telephone network that is connected to the interfacing part 73-11 and terminals (hereinafter referred to simply as “accommodated terminals”) that can be an originating party or a destination party of a telephony call among the terminals connected to the LAN 61-11 are stored in the address table 84-11 in advance.
The accommodated terminal is not limited to the telephone set and includes various kinds of communication terminals that can be used for multimedia transmission services, such as the facsimile terminal, image terminal, data terminal, and mobile terminal (including terminals conforming to IMT-2000 etc.). Further, the accommodated terminal is not limited to terminals that sends and receives a speech signal in an audio frequency band.
As shown in FIG. 16, the state management table 85-11 is a storage area where to store an array of records each being a combination of the following pieces of information:                An originating terminal identifier (may be either a telephone number or an IP address) indicating an accommodated terminal where a telephony originating call that has occurred is persisting among he above-mentioned accommodated terminals.        A co-caller identifier (may be either a telephone number or an IP address) indicating an accommodated terminal (may be one that is accommodated by a base other than the base that accommodates the originating terminal) that is the co-caller of the accommodated terminal indicated by the originating terminal identifier.        State information indicating the states of the accommodated terminals indicated by the originating terminal identifier and the co-caller identifier, the type (e.g., an originating call or a termination call) of the call concerned, and an identifier indicating the call.        
The hardware configurations of the bases 60-12, 60-21, 60-22, 60-31, and 60-32 are the same as the hardware configuration of the base 60-11, and hence will not be described. A notation will be employed in which components in the bases 60-12, 60-21, 60-22, 60-31, and 60-32 corresponding to a component in the base 60-11 are given the same reference numeral as the latter plus suffixes “12,” “21,” “22,” “31,” and “32” that replace the suffix “11.”
In the conventional example having the above configuration, when, for example, an accommodated terminal that is accommodated by the base 60-11 originates a call to an accommodated terminal that is accommodated by the base 60-21 to cause a telephony call, the individual parts cooperate in the following manner.
In the base 60-11, the terminal processing part 71-11 sends, to the gatekeeper 80-11, via the LAN 61-11, a message ARQ that contains an originating terminal identifier indicating the accommodated terminal as the originating party and a co-caller identifier indicating the accommodated party as the destination party and that is an inquiry about permission/refusal of origination (indicated by symbol (1) in FIG. 17).
The gatekeeper 80-11 (processor 82-11) judges whether the state management table 85-11 does not have a record in which the value of the state information means that the call is persisting and that satisfies any of the following conditions (indicated by symbol (2) in FIG. 17):                The value of the originating terminal identifier field or the co-caller identifier field is equal to the value of the originating terminal identifier that is contained in the message ARQ.        The value of the originating terminal identifier field or the co-caller identifier field is equal to the value of the co-caller identifier that is contained in the message ARQ.        
In the following description, the above judgement will be called “first judgement.”
The gatekeeper 80-11 further performs the following series of operations:                Spirits the value of the co-caller identifier contained in the message ARQ according to a predetermined numbering plan (or rules relating to the allocation of IP addresses to the individual terminals accommodated by the bases 60-11 to 60-32), and acquires a base identifier indicating a base (hereinafter referred to as “counter base”) where the terminal indicated by the co-caller identifier is accommodated.        Determines the number c of records in which the base indicated by the value of the co-caller identifier field is indicated by the above base identifier among the records of the state management table 85-11.        Judges whether the following inequality is satisfied for the number c of records and a maximum number N (it is assumed here that the maximum number N is given in advance as a known number) of speech signals that can be transmitted parallel as a sequence of IP datagrams via the internode link 63-11 formed between the base 60-11 and the base indicated by the base identifier. In the following description, the above judgement will be called “second judgement.”c≦N−1        
The gatekeeper 80-11 further sends the terminal processing part 71-11 a message ACF/ARJ indicating the AND of the results of the first and second judgements (indicated by symbol (3) in FIG. 17). Only when the AND value is true, the following operations are performed on one empty record of the state management table 85-11:                Seizes a record (hereinafter referred to as “reservation record”) by appending predetermined control information to the state information field.        Stores the originating terminal identifier that is included in the message ARQ in the originating terminal identifier field.        Stores the co-caller identifier that is included in the message ARQ in the co-caller identifier field.        The terminal processing part 71-11 recognizes the message ACF/ARJ, that is, the above-mentioned AND value and suspends the call setup for the call concerned if the AND value is false.        
However, when the AND value is true, the terminal processing part 71-11 acquires the IP address of the gatekeeper 80-21 in the base 60-21 where the terminal to become the destination party by referring to the value of the IP address field (hereinafter referred to as “destination party IP address”) of the record corresponding to the co-caller identifier that is included in the message ARQ among the records of the address table 84-11 (indicated by symbol (4) in FIG. 17).
For example, the IP address of the gatekeeper 80-21 is acquired by performing one of the following operations:                The gatekeeper 80-21 has a database in which the unique gatekeeper IP address corresponding to the above destination party IP address is registered in advance. The IP address of the gatekeeper 80-21 is acquired by referring to this database.        Each gatekeeper (including the gatekeeper 80-21) has a database in which the IP addresses of the terminals accommodated by itself are registered in advance. The gatekeeper 80-21 broadcasts, to the other gatekeepers, packets that are an inquiry including the above destination party IP address, and extracts the IP address of the gatekeeper 80-21 from a predetermined field of packets that are received as a response to the inquiry packets.        
However, the above operation can be realized by using various known communication protocols and is not an essential feature of the invention, and hence will not be described any further.
By cooperating with the gatekeeper 80-21 having the above IP address and other processing blocks via the LAN 61-11, the router 62-1, the internode link 63-12, the router 62-2, and the LAN 61-21, the terminal processing part 71-11 judges permission/refusal of termination at the terminal indicated by the above-mentioned co-caller identifier.
The procedure of the processing that is performed by the gatekeeper 80-21 to realize the above judgement is irrelevant to the invention and can be realized by using various known techniques, and hence will not be described.
When the judgement result is false, the terminal processing part 71-11 suspends the call setup for the call concerned.
On the other hand, when the judgement result is true, the terminal processing part 71-11 continues the call setup by exchanging, in the form of IP packets (IP datagrams), predetermined control information with the gatekeeper 80-11 and the gatekeeper 80-21 and the gateway 70GW-21 (indicated by symbol (8) in FIG. 17).
When the call concerned has become a successful call (i.e., a call with which the co-caller has made a response and thereby a state has been established that the co-caller and the originating party can exchange a speech signal), between the bases 60-11 and 60-21 a speech signal of the successful call is transmitted via the router 62-1, the internode link 63-12, and the router 62-2 in the form of a sequence of IP datagrams (indicated by symbol (9) in FIG. 17).
During the course of the above call setup, the gatekeepers 80-11 and 80-12 refer to the address tables 84-11 and 84-21 when necessary and update the values of the individual fields of the state management tables 85-11 and 85-21 according to the procedure of the call setup.
When the originating party (or destination party) is not a terminal that is accommodated by the LAN 61-11 (or 61-21), the individual parts of the gateway 70GW-11 (or 70GW-21) perform the following operations:                The interfacing part 73-11 (or 73-21) performs interfacing that relate to exchange of a signaling signal, a register signal, and a speech signal according to a signaling scheme suitable for the originating party (or destination party).        The protocol converting part 72-11 (or 72-21) maintains conditions under which the originating party (or destination party) that is accommodated via the interfacing part 73-11 (or 73-21) is equivalent to a terminal that is accommodated by the LAN 61-11 (or 61-21) during the course of the call setup and the exchange of the speech signal by performing, in a reversible manner, predetermined conversion processing on the signaling signal, register signal, and speech signal.        
Therefore, the call setup for the above telephony call is continued only when the internode link 63-12 that is provided between the bases 60-11 and 60-21 that accommodate the originating party and the destination party of the call, respectively, via the routers 62-1 and 62-2 have a surplus bandwidth, and a speech signal of the call is transmitted via the internode link 63-12 as a sequence of IP datagrams.
Surplus bandwidths of the internode links 63-12 and 63-23 are secured as bandwidths to be used for transmission of a speech signal of a telephony call even in a case where a WAN (wide area network) having a narrow bandwidth such as a VPN (virtual private network) is used for the internode links 63-12 and 63-23. Therefore, the speech quality is kept high in a stable manner though a speech signal is transmitted via a best effort type or connectionless network.
In the conventional example described above, the judgement as to whether a bandwidth to be used for transmission of a speech signal of a telephony successful call that has newly occurred can be secured within a surplus bandwidth of an internode link is performed based on the following assumptions by determining which of the number of successful calls that can persist parallel for respective combinations of bases that accommodate the originating party and the destination party of each successful call, respectively, and a maximum number (equal to the above-mentioned number N) that conforms to the transmission capacity of the internode link is larger:                Bandwidths to be used for the transmission of speech signals of respective successful calls are the same and are kept constant.        Only one internode link is provided between the bases that accommodate an originating party and a destination party, respectively, and the transmission capacity of each internode link is kept constant.        
However, for example, the speech signal that is transmitted via the internode link 63-12 as a sequence of IP datagrams may include not only a speech signal to be transmitted between terminals located in the respective bases 60-11 and 60-21 but also a speech signal to be transmitted between a terminal located in one of the bases 60-11 and 60-12 and a terminal located in one of the bases 60-21, 60-22, 60-31, and 60-32.
That is, although the traffic volumes of the internode links 63-12 and 63-23 are not necessarily the same, surplus transmission bandwidths of the respective internode links 63-12 and 63-23 are not recognized individually.
Therefore, the criteria for the above-described second judgement are not necessarily proper as criteria for the judgement as to whether a bandwidth that is necessary for the transmission of a speech signal of a successful call that newly occurs can be actually secured within a surplus bandwidth of the internode link 63-12.
Further, in the conventional example, it is possible that one of the internode links 63-12 and 63-23 is congested due to concentration of much more traffic on it than on the other and, as a result, the speech quality and the transmission quality deteriorate.